Shadow thermoprinting



c. A. KUHRMEYER ETAL 2,919,349

SHADOW THERMOPRINTING Filed April 2, 195a Dee. 29, 1959 so area of fdd/d/IT energy /6 7 graph/c original /0 /.5'-- hem -5ens/'7/'re C 0,05/ paper [/v vm/ o/as CAPL A. KUBPMEYEP- D L 6. IOMBLE CARL 5. MILLER ATTOPMEyJ Unite States atent 7 2,919,349 SHADOW THERMOPRINTIN G ApplicationApril 2, 1956, Serial No. 575,434 3 Claims. Cl. 250-65) This invention relates to the reproduction of printed matter or the like on heat-sensitive copying-paper by a novel method which is here termed shadow thermoprinting. The method involves the application of intense radiant energy through the relatively transparent inkfree areas of a printed page or other graphic subject-matter of which a copy is desired and to a rapidly-reactive heat-sensitive copy-paper which is capable of absorbing said radiant energy. The radiant energy is converted to heat energy within the heat-sensitive copy-paper in apattern determined by the graphic subject-matter, resulting in the formation of visible copy in the copying-paper.

This invention is related to' the invention described and claimed in the copending application of Carl S. Miller, Serial No. 747,338, filed May 10, 1947, now Patent No. 2,740,896.

The invention has particular utility in aifording means for rapidly obtaining one or more copies of printed matter, diagrams, photographs, or other graphic'subject-matter directly from the original. There is involved merely the proper positioning of the sensitive copy-paper with respect to the original, and the exposure of the original to intense radiant energy. A true copy is produced directly, with no necessity of subsequent development of a latent image or of other processing. Both negative and positive copies are easily made.

The invention is applicable to the copying of any type of original document carrying visible copy, including painted, inked, or dyed as well as printed or typewritten originals, where the substrate or background material is capable of transmitting a substantial portion of the radiant energy employed. Messages Written on transparent films, paper and the like with inks of all colors have been copied, as have messages produced by hectographic processes and consisting of organic dyes transferred to the surface of white paper.

The attached drawing, which is not necessarily to scale, illustrates in cross-section a strip of heat-sensitive copypaper 10 beneath a graphic original 11 which is irradiated with intense radiant energy from a lamp source 13. The copy-paper is here shown to consist of a backing or carrier member 14 and a heat-sensitive layer 15. The graphic original has inked portions 16 and ink-free surface areas 17, and is transmissive of radiant energy produced by lamp 13. When the lamp is flashed, there is directly produced in the strip 10 a negative copy of the 5 graphic subject-matter of the original 11; that is, the

areas of the heat-sensitive layer beneath the ink-free areas 17 are visibly changed, as illustrated in the drawing.

High-intensity photoflash bulbs provide a useful source of high-intensity radiant energy, but other sources having still higher output of radiant energy are preferred.

One such source, indicated in the drawing, consists of a quartz or Pyrex glass tube about ten inches long, having an electrode at each end, filled with xenon or other inert gas under reduced pressure, and externally wound with an open wire spiral. The spiral is connected to a 20,000 volt spark coil while the electrodes of the flash 2,919,349 Patented Dec. 29, 1959 closing the circuit to the spark coil, results in an intense flash having a duration of about 1000 microseconds, with peak intensity at about 100 microseconds. Intensity is high in the infra-red, and particularly high in the visible regions.

The flash source just described has been found effective in the copying of many different. types of graphic subject-matter on radiation-absorptive heat-sensitive copying-paper by the procedures here described.

The heat-sensitive copying-paper may desirably consist of a paper backing or carrier sheet coated with-a thin layer of a dispersion of ferric stearate and gallic acid in a solution of ethyl cellulose binder, and dried at moderate temperatures. 0

The coating is initially a faint tan, changing almost instantaneously to a brownish black when heated to about -120 C. 'It is greatly improved for the purposes of this invention by adding'small amounts. of pigments to the heat-sensitive coating. Both titanium dioxide-and carbon -black, as well as many colored pigments, are ef-, fective, but light-colored pigments provide improved contrast as well as increasing theabsorption of the radiant energy in the heat-sensitive layer. However the nonpigmented product is also useful, particularly since a sup porting panel or the like is ordinarily placed beneath the copy-paper 10' and serves to reflect to the heat-sensitive layer much of any radiant energy passing through the copy-paper.

Another specific example of a heat-sensitive coating containsa dispersion of gum guaiac and cerium stearate in a solution of ethyl cellulose binder, together with pigments as desired. The resulting dried coating is initially light in color. It converts to a stable dark-colored modification on brief heating, but is then rendered permanently light-colored by; further heating. The sheet is therefore uniformly converted to the dark-colored modification before exposure; When exposed to the radiant energy through a graphic black-on-White original, a positive copy, having blue lines on a yellowish background, is obtained.

Useful reproductions of graphic subject-matter may also be obtained by shadow thermoprinting processes on radiation-absorptive heat-sensitive copying-papers comprising a dark or colored substrate obscured with a thin masking layer of particles of normally transparent fusible material, e.g. waxes or waxy materials, secured to the substrate and protected from oflfsetting with a non-fusing binder. A radiation-absorbent pigment or dye may be dispersed within the layer of fusible particles, but is not ordinarily required since the waxy layer is itself highly absorptive of light in the visible region.

Many other radiation-absorptive heat-sensitive copying-sheets are useful in the practice of this invention, those described hereinabove being given as illustrative rather than limitative examples.

Paper, film, fabric, wood, and many other materials are effective as backing or carrier elements for the heat sensitive coating, although thin flexible sheet material such as paper is ordinarily preferred. The backing may absorb, reflect, or transmit the radiant energy. However the sheet must be capable of absorbing the energy which is then converted to heat and utilized in producing the desired visible change. Ordinarily such absorption of energy will occur directly within the heat-sensitive layer.

The ability to obtain clear and sharp reproductions of graphic subject-matter has been found to be dependent on both the duration of the flash radiation and the intensity of the flash in the visible region. The lamp systern described hereinbefore is highly eitective and is illustrative.

Suitable optical systems may be devised to increase the uniformity of radiation. The copy area is easily increased either by employing a number of flash tubes operating simultaneously, or by flashing a single tube at suitable intervals over the area involved. Flash tubes may be provided with flattened and extended surfaces for increased uniformity of irradiation.

Referringagain to the drawing, it is apparent that radiation from the source 13 will be absorbed in the inked areas 16 of the original and there converted to heat energy. It is observed, however, that no visible 7 said original a rapidly-reactive heat-sensitive copy-sheet change occurs in areas of the copy-paper corresponding to these inked areas 16, whereasthe heat-sensitive layer is converted to a visibly different from at areas corresponding to ink-free surface areas 17 of the original. It appears probable that the heat energy obtained in the linked areas is difiused and prevented from reaching the heat-sensitive layer by the backing 11, which acts as a heat-insulation barrier. Loss of heat of radiation from the inked areas is also believed to be high, due to the extreme intensity of the flash discharge. Where extremely thin or highly heat-conductive transparent sheet material forms the sheet 11, it may be found desirable to place some additional heat barrier member between sheet 11 and copy-paper 10 thin silk bolting-cloth is useful for this purpose. The original should'be kept as close as possible to the copy-paper in order to prevent diffusion of the image-carrying energy. With sufiiciently high intensity and short duration of flash, the heat-barrier layer may be omitted.

The above discussion is offered in probable explana tion of the effects produced. But regardless of theory, the shadow thermoprinting method here described, using radiation-absorptive heat-sensitive copying-papers and high-intensity rapid-flash sources of radiant energy, has been found to produce clear and sharp copies of all types of graphic originals having visible graphic subjectmatter applied to paper, film, or other thin carrier web which is transmissive of the radiant energy.

7 What is claimed is as follows:

1. A method for the direct production of a permanent facsimile copy of a graphic original having visibly dilferent areas providing differential transmissivity of radiant energy through said original, comprising placing beneath which is absorptive of said radiant energy, and exposing said original to a high intensity rapid flash of said radiant energy, the intensity and time of radiation being so selected as to cause selective heating and develop an immediate visible change in areas of said copy-sheet corresponding to the more transmissive areas of said original, while avoiding any significant visible change in the remaining areas.

2. A method for the direct production of a permanent facsimile copy of a graphic original having areas absorptive of radiant energy with increase in temperature, and other visibly difierent areas transmissive of said radiant energy, comprising placing beneath said original a rapidly-reactive heat-sensitive copy-sheet which is absorptive of said radiant energy, and exposing said original to a high intensity rapid flash of said radiant energyat sufficiently high intensity and for sufliciently short time to cause selective heating of, and immediate visible change in,areas of the copy paper corresponding to transmissive areas of the original while avoiding visible change in areas corresponding to absorptive areas of the original.

3. A method for the direct production of a permanent facsimile copy of a graphic original comprising a thin sheet material readily transmissive of radiant energy and having visibly distinct printed areas which are absorptive of said radiant energy, with increase in temperature, said method comprising (a) placing beneath said original, in order, a thin heat-insulating sheet'material transmissive of said radiant energy, and a rapidly-reactive heat-sensitive copy-sheet which is absorptive of said radiant energy, and (b) exposing said original to a high intensity rapid flash of said radiant energy at sufiiciently high intensity and for sufliciently short time to cause selective heating of, andvisible change in, areas of the copy-paper corresponding to transmissive areas of the original while avoiding visible change in areas corresponding to absorptive areas of the original.

Miller et al. July 22, 

